Active clamping with bootstrap circuit

ABSTRACT

An active clamp circuit for a power converter having a transformer includes a switch having a drain node, a gate node, and a source node, the drain node configured to be connected to a first terminal of a primary winding of the transformer, a capacitor having a first terminal connected to the source node, and a second terminal to be connected to a second terminal of the primary winding, a gate driver coupled to the gate node to control the switch and having a high-side input node and a low-side input node, the low-side input node being coupled to the first terminal of the capacitor, and a voltage regulator to: i) receive an input voltage from the second terminal of the capacitor, and ii) provide a regulated voltage to the high-side input node using the input voltage and being of a sufficient voltage level to control the switch.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.16/145,819, filed on Sep. 28, 2018, and entitled “Integrated Self-DrivenActive Clamp”, and is additionally related to U.S. patent applicationSer. No. 16/247,227, filed Jan. 14, 2019, and entitled “Active ClampCircuit”, both of which are hereby incorporated by reference for allpurposes.

BACKGROUND

Switch-mode power supplies (“power converters”) are power managementcomponents in modern electronic devices. They provide, among otherthings, efficient and galvanically isolated power to multiple loads. Toachieve high power processing efficiency and/or galvanic isolation,conventionally one or more magnetically coupled elements, semiconductorswitches and associated gate driver circuits are required.

The magnetically coupled elements often suffer from non-trivial leakageinductance phenomena, which necessitate the need for affordable voltagesnubber circuits to control the semiconductor switch peakdrain-to-source voltages. Recycling of energy using an active clampingconfiguration within the power converter provides an opportunity forpower converter form-factor reduction and power efficiency improvement.

Active clamping configurations typically include one or moresemiconductor switches and associated gate drivers. When n-channelMOSFET semiconductor devices are used to implement the one or moresemiconductor switches, the associated gate drivers may require avoltage that is higher than that of a DC input voltage supplied to thepower converter. In such configurations, a “bootstrap” circuit is oftenused to generate the required higher voltage.

SUMMARY

In some embodiments, an active clamp circuit for a power converterhaving a transformer includes an active clamp switch having a drainnode, a gate node, and a source node, the drain node being configured tobe electrically connected to a first terminal of a primary winding ofthe transformer. The active clamp circuit further includes an activeclamp capacitor having a first terminal electrically connected to thesource node of the active clamp switch, and a second terminal configuredto be electrically connected to a second terminal of the primarywinding. The active clamp still further includes a gate driver circuitcoupled to the gate node to control the active clamp switch, the gatedriver circuit having a high-side input voltage node and a low-sideinput voltage node, the low-side input voltage node being coupled to thefirst terminal of the active clamp capacitor. The active clamp circuitstill yet further includes a voltage regulator circuit configured to: i)receive an input voltage from the second terminal of the active clampcapacitor, and ii) provide a regulated voltage to the high-side inputvoltage node of the gate driver circuit using the input voltage, theregulated voltage being of a sufficient voltage level to control theactive clamp switch.

In some embodiments, a power converter includes a transformer having aprimary winding and a secondary winding, a first terminal of the primarywinding being configured to be coupled to a DC voltage input node, thesecondary winding being configured to be coupled to a load, a mainswitch coupled to a second terminal of the primary winding to control acurrent through the primary winding, and an active clamp circuit. Theactive clamp circuit includes an active clamp switch having a drainnode, a gate node, and a source node, the drain node being configured tobe electrically connected to the first terminal of the primary windingof the transformer. The active clamp circuit further includes an activeclamp capacitor having a first terminal electrically connected to thesource node of the active clamp switch, and a second terminal configuredto be electrically connected to the second terminal of the primarywinding. The active clamp circuit still further includes a gate drivercircuit coupled to the gate node to control the active clamp switch, thegate driver circuit having a high-side input voltage node and a low-sideinput voltage node, the low-side input voltage node being coupled to thefirst terminal of the active clamp capacitor. The active clamp circuitstill yet further includes a voltage regulator circuit configured to: i)receive an input voltage from the second terminal of the active clampcapacitor, and ii) provide a regulated voltage to the high-side inputvoltage node of the gate driver circuit using the input voltage, theregulated voltage being of a sufficient voltage level to control theactive clamp switch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a power converter having an activeclamp circuit, in accordance with some embodiments.

FIG. 2 is a simplified schematic of an example active clamp circuit witha bootstrap circuit that could be used in the power converter shown inFIG. 1.

FIG. 3 is a simplified schematic of an example improved active clampcircuit with an improved bootstrap circuit for use in the powerconverter shown in FIG. 1, in accordance with some embodiments.

DETAILED DESCRIPTION

Some embodiments described herein provide an improved active clampcircuit with an improved bootstrap circuit for use in a power converterthat converts an input voltage to an output voltage using a transformer.In some embodiments, the improved bootstrap circuit is advantageouslyimplemented without requiring an additional high-breakdown voltagediode. Additionally, in some embodiments, the improved bootstrap circuitis advantageously implemented without requiring a separate input voltage(i.e., V_(CC)), thus simplifying the overall power converter designand/or active clamp integration.

In power converters sensitive to power losses and heat generation,energy dissipation in lossy components in the form of heat isundesirable. Thus, recycling of energy using an active clampingconfiguration within the power converters provides an opportunity forpower converter form-factor reduction and power efficiency improvement.Active clamp circuits, as compared to resistor-capacitor-diode (RCD)snubber circuits, advantageously increase power processing efficiency ofthe power converter by recycling energy stored in a leakage inductanceof the transformer. Additionally, such active clamp circuits clamp aprimary side peak voltage of a main switch of the power converter, whichenables the power converter to utilize primary side switches having alower voltage rating, leading to reduced power losses during switchconduction and/or switching.

In some embodiments disclosed herein, an n-channel MOSFET (NMOS) switchis used to implement an active clamp switch of an active clamp circuitof a power converter. NMOS switches advantageously have a loweron-resistance as compared to p-channel MOSFET (PMOS) devices. However,to fully turn an NMOS switch on (i.e., an ON-state whereby a channelregion of the NMOS switch is conducting), a sufficient gate-sourcevoltage of the NMOS switch is required.

As disclosed herein, an improved bootstrap circuit is used to generatethe gate-source voltage required to control, by a gate driver circuit,the on/off state of an active clamp switch of an active clamp circuit.As disclosed herein, the improved bootstrap circuit does not require ahigh-breakdown voltage diode which is often required for conventionalbootstrap circuit architectures. Additionally, as disclosed herein, theimproved bootstrap circuit does not require a second voltage supply(e.g., V_(CC)) which is often required by conventional bootstrap circuitarchitectures.

FIG. 1 is a simplified circuit schematic of a power converter 100, inaccordance with some embodiments. Some elements of the power converter100 have been omitted from FIG. 1 to simplify the description of powerconverter 100 but are understood to be present. A voltage source V_(in)′is received at the power converter 100. V_(in)′ can be provided eitheras an alternating current (AC) or direct current (DC). An input side ofthe power converter 100 generally includes an input voltage filter block122, a rectifier block 116 (in the case of AC input), an input voltagebuffer capacitor C1, an active clamp circuit 114 (which includes an NMOSactive clamp switch M3), a main switch M1 driven by apulse-width-modulation (PWM) signal PWM_(M1), and a primary sidecontroller circuit 118. The input voltage filter block 122, therectifier block 116 and the input buffer capacitor C1 provide afiltered, buffered, rectified, or otherwise conditioned input voltageV_(in) (i.e., a DC input voltage at a DC voltage input node) to atransformer 102.

The transformer 102 transfers power from the input side of the powerconverter 100 to an output side of the power converter 100 and generallyincludes a primary winding 104 with a first terminal 108 and a secondterminal 110. The output side of the power converter 100 generallyincludes a secondary winding 106 of the transformer 102, an outputbuffer circuit 112, a synchronous rectifier switch M2, a synchronousrectifier switch controller circuit 120, and is configurable to beconnected to a load R_(L).

The first terminal 108 of the primary winding 104 receives the DC inputvoltage V_(in). The second terminal 110 of the primary winding 104 iscoupled to a drain node of the main switch M1 and to an input of theactive clamp circuit 114. The main switch M1 controls a current throughthe primary winding 104 to charge a magnetizing inductance L_(M) 105 ofthe transformer 102 during a first portion of a switching cycle of thepower converter 100. The synchronous rectifier switch M2 controls acurrent flow through the secondary winding 106 to discharge thetransformer 102 into the output buffer circuit 112 and the load R_(L)during a subsequent portion of the switching cycle.

When the main switch M1 is enabled by the primary side controllercircuit 118 during the first portion of a switching cycle, current flowsthrough the primary winding 104 to a voltage bias node such as ground,illustrated in FIG. 1 as a triangle coupled to a source node of the mainswitch M1. The current flow through the primary winding 104 causesenergy to be stored in the magnetizing inductance L_(M) 105 and aleakage inductance L_(L) (not shown) of the transformer 102. When themain switch M1 is disabled in a subsequent portion of the switchingcycle, an output voltage V_(out) is generated at the output buffercircuit 112 and is provided to the load R_(L). When the main switch M1is turned off, a reflected voltage (nV_(out)) is developed at theprimary winding 104. The contribution of the reflected voltage nV_(out)to a drain-source voltage V_(dsM1) of the main switch M1 at the secondterminal 110 is expressed as:V _(dsM1) =nV _(out)  (Equation 1)where n is a turns ratio of the transformer 102. Energy stored in theleakage inductance L_(L) of the transformer 102 also contributes to thevoltage V_(dsM1) developed at the second terminal 110. The active clampcircuit 114 prevents the voltage V_(dsM1) from increasing to a levelthat damages the main switch M1.

FIG. 2 is a simplified circuit schematic of an active clamp circuit 214that could be used to implement the active clamp circuit 114 of FIG. 1,but which has some disadvantages that the present invention mitigates oreliminates. The active clamp circuit 214 generally includes the activeclamp switch M3, an active clamp capacitor C3, a gate driver circuit 230having a high-side input voltage node (+) and a low-side input voltagenode (−), and a simplified implementation of a conventional bootstrapcircuit 232. The active clamp switch M3 has a gate node (G), a drainnode (D) and a source node (S). Some circuit elements have been omittedfrom the schematic for simplicity.

The conventional bootstrap circuit 232 generally includes a resistorR_(Boot), a high-breakdown voltage diode D_(Boot), and a bootstrapcapacitor C_(Boot). Also shown are the terminals 108, 110 of the primarywinding 104 of the transformer 102 introduced with reference to FIG. 1,and a node 236.

In order to fully turn the active clamp switch M3 on (i.e., control theactive clamp switch M3), the gate driver circuit 230 must drive the gatenode G of the active clamp switch M3 with a gate-source voltage that ishigher than a turn-on threshold of the active clamp switch M3 (e.g.,generally a voltage higher than a voltage at the source node S of theactive clamp switch M3). Because the source node S of the active clampswitch M3 is coupled to the second terminal 110 of the primary winding104, the voltage at the source node S of the active clamp switch M3 willequal to V_(dsM1). Thus, to fully turn on the active clamp switch M3, avoltage higher than V_(dsM1) is required. However, as previouslydescribed with reference to equation 1, the voltage V_(dsM1) may behigher than the input voltage V_(in) during portions of the switchingcycle.

Thus, the conventional bootstrap circuit 232 is utilized to provide avoltage V_(DDA) to the gate driver circuit 230 to control the activeclamp switch M3. The voltage V_(DDA) is as high or higher than theturn-on threshold of the active clamp switch M3 so that the gate drivercircuit 230 can fully turn on the active clamp switch M3 in response toan active clamp control signal PWM_(M3) which is provided by a module orcircuit (not shown) of the power converter 100 or the active clampcircuit 214. The voltage V_(DDA) is referenced to the terminal 110(i.e., V_(DD)A has a floating ground). A supply voltage V_(CC) isconventionally generated using another voltage regulator circuit (notshown) of the power converter 100, for example, using a voltageregulator that generates the voltage V_(CC) based on a current receivedfrom an auxiliary winding (not shown) of the transformer 102.

The resistor R_(Boot) generally protects the conventional bootstrapcircuit 232 and the gate driver circuit 230 from high in-rush currents.In operation, when the main switch M1 of the power converter 100 is on(and the active clamp switch M3 is off), the terminal 110 is pulled toground (i.e., a bias voltage coupled to the source node of the mainswitch M1). During this time, the voltage V_(CC) charges the capacitorC_(Boot) through the resistor R_(Boot) and the diode D_(Boot). Thus,node A of the bootstrap capacitor C_(Boot) is charged to approximatelyV_(CC). At a subsequent time in the switching cycle, when the mainswitch M1 is turned off, the voltage developed at the bootstrapcapacitor C_(Boot) is pulled up by voltage V_(dsM1) developed at thenode 236 (as discussed with reference to equation 1). Thus, the voltageat node A, and correspondingly the voltage V_(DDA), reaches a voltagelevel (approximately V_(CC)+V_(dsM1)) which is sufficient to fully turnthe active clamp switch M3 on.

Unfortunately, high-breakdown voltage diodes such as the diode D_(Boot)can be both large as well as costly and may preclude integrating theactive clamp circuit 214 into a single integrated circuit (IC).Additionally, especially in the systems where the active clamp circuit114 is implemented as a self-driven clamp module, providing the voltageV_(CC) to the active clamp circuit 214 may introduce design complexityto the power converter 100.

FIG. 3 is a simplified circuit schematic of an improved active clampcircuit 314 that implements the active clamp circuit 114 of FIG. 1, inaccordance with some embodiments. The improved active clamp circuit 314generally includes the NMOS active clamp switch M3, the active clampcapacitor C3, a gate driver circuit 330 having a high-side input voltagenode (+) and a low-side input voltage node (−), and an improvedbootstrap circuit 334. The improved bootstrap circuit 334 generallyincludes a voltage regulator circuit 338 (e.g., an LDO or other linearpower regulator that is configured to lower/reduce and/or limit areceived input voltage) and an optional capacitor 340 that isconfigurable to be coupled across the high-side input voltage node (+)and the low-side input voltage node (−) of the gate driver circuit 330.Also shown are the terminals 108, 110 of the primary winding 104 of thetransformer 102 described with reference to FIG. 1, and terminals 336,342 of the active clamp capacitor C3. Some circuit elements have beenomitted from the circuit schematic for simplicity.

The improved bootstrap circuit 334 advantageously does not require anadditional power source (i.e., to provide the voltage V_(CC)) ascompared to the conventional bootstrap circuit 232. Additionally, theimproved bootstrap circuit 334 advantageously does not require ahigh-breakdown voltage diode (i.e., the diode D_(Boot)) as compared tothe conventional bootstrap circuit 232. Thus, the improved bootstrapcircuit 334 can advantageously be integrated into a single IC. In someembodiments, the improved bootstrap circuit 334 is integrated into asingle IC along with the remaining circuit components of the activeclamp circuit 314 (i.e., the active clamp switch M3, the voltageregulator circuit 338, and the gate driver circuit 330).

As shown, a connection arrangement of the active clamp capacitor C3disclosed in FIG. 3 differs as compared to a connection arrangement ofthe active clamp capacitor C3 shown in FIG. 2. As shown in FIG. 3, theactive clamp capacitor C3 is connected between the source node S of theactive clamp switch M3 and the second terminal 110 of the primarywinding 104 of the transformer 102 and is thereby connected to the drainnode of the main switch M1. In contrast, the active clamp capacitor C3shown in FIG. 2 is connected between the drain node D of the activeclamp switch M3 and the first terminal 108 of the primary winding 104 ofthe transformer 102.

The active clamp switch M3 is controlled based on an active clampcontrol signal PWM_(M3) via the gate driver circuit 330. The activeclamp control signal PWM_(M) 3 is provided by a module or circuit (notshown) of the power converter 100 or of the improved active clampcircuit 314. The active clamp circuit 314 clamps the voltage V_(dsM1) atthe drain node of the main switch M1 to a maximum voltage (e.g., withina safe operating range of the main switch M1). In order to fully turnthe active clamp switch M3 on in response to the control signalPWM_(M3), the gate driver circuit 330 must drive the gate node G of theactive clamp switch M3 with a gate-source voltage that is higher than aturn-on threshold of the active clamp switch M3 (e.g., generally higherthan a voltage Vs at the source node S of the active clamp switch M3).

The improved bootstrap circuit 334 advantageously provides a high-siderail voltage V_(DDA) to the high-side input voltage node (+) of the gatedriver circuit 330, the voltage V_(DDA) being as high or higher than theturn-on threshold (i.e., higher than a voltage at the source node S) ofthe active clamp switch M3, such that the gate driver circuit 330 canfully turn the active clamp switch M3 on without requiring ahigh-breakdown voltage diode and without requiring an external voltagesource (e.g., V_(CC)). The high-side rail voltage V_(DD)A is referencedto a bias voltage V_(SSA) (i.e., a low-side rail voltage) at thelow-side input voltage node (−) of the gate driver circuit 330 which isconnected to the terminal 342 of the active clamp capacitor C3. Thus,the voltage V_(DDA) is referenced to a floating ground which isdifferent than a ground of the power converter 100 (e.g., at a sourcenode of the main switch M1). The voltage regulator circuit 338 isconfigured to lower, buffer, condition, or limit the input voltagereceived by the voltage regulator circuit 338 such that the voltageV_(DDA) output by the voltage regulator circuit 338 is lowered and/orlimited as compared to the voltage received by the voltage regulatorcircuit 338 from the terminal 336 of the active clamp capacitor C3.

During a portion of a switching cycle of the power converter 100 inwhich the main switch M1 is in an OFF state (i.e., not conducting), theterminal 110, and thereby the terminal 336, develops a voltageV_(dsM1)=nV_(out) as discussed with reference to equation 1. During thisportion of the switching cycle, the active clamp capacitor C3 is chargedby a reverse current flow i_(sd) from the terminal 110 to the terminal108 via a body diode of the active clamp switch M3. As the active clampcapacitor C3 is charged, a voltage V_(C3) develops across the activeclamp capacitor C3 (i.e., across the terminals 336, 342), the voltageV_(C3) when measured across the active clamp capacitor C3 beingapproximately equal to nV_(out).

The voltage regulator circuit 338 receives the voltage difference V_(C3)from across the terminals 336, 342 of the active clamp capacitor C3. Thevoltage regulator circuit 338 uses the voltage V_(C3) developed acrossthe active clamp capacitor C3 to generate the high-side rail voltageV_(DDA), which is received at the high-side input voltage node (+) ofthe gate driver circuit 330, by lowering, buffering, limiting, orotherwise conditioning the voltage V_(C3). The bias voltage V_(SSA) isreceived by the gate driver circuit 330 at the low-side input voltagenode (−) from the terminal 342 of the active clamp capacitor C3. Thesource node S of the active clamp switch M3 and the low-side inputvoltage node (−) of the gate driver circuit 330 are both coupled to theterminal 342 of the active clamp capacitor C3, and are thus both at alower voltage relative to V_(DDA) and further are of a different voltagelevel than a voltage at a ground node of the power converter 100 (e.g.,at the source node of the main switch M1). Thus, the gate driver circuit330 can provide a sufficient gate voltage to the gate node G to fullyturn on the active clamp switch M3. The optional capacitor 340 is usedin some embodiments to buffer the voltage V_(DDA) received at the gatedriver circuit 330.

At a subsequent time in the switching cycle, the active clamp switch M3is turned off and the main switch M1 is turned on. There is a durationof time before this transition during which both the active clamp switchM3 and the main switch M1 are both turned off. The duration of timeduring which the active clamp switch M3 and the main switch M1 are bothturned off depends on a desired system operation of the power converter100. At the subsequent time in the switching cycle when the main switchM1 is turned on and the active clamp switch M3 is turned off, theterminal 110, and thereby the terminal 336, is pulled to ground. Theswitching cycle is repeated when the main switch M1 is turned off again,and the active clamp capacitor M3 is charged once again by the currenti_(sd).

Reference has been made in detail to embodiments of the disclosedinvention, one or more examples of which have been illustrated in theaccompanying figures. Each example has been provided by way ofexplanation of the present technology, not as a limitation of thepresent technology. In fact, while the specification has been describedin detail with respect to specific embodiments of the invention, it willbe appreciated that those skilled in the art, upon attaining anunderstanding of the foregoing, may readily conceive of alterations to,variations of, and equivalents to these embodiments. For instance,features illustrated or described as part of one embodiment may be usedwith another embodiment to yield a still further embodiment. Thus, it isintended that the present subject matter covers all such modificationsand variations within the scope of the appended claims and theirequivalents. These and other modifications and variations to the presentinvention may be practiced by those of ordinary skill in the art,without departing from the scope of the present invention, which is moreparticularly set forth in the appended claims. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to limit the invention.

What is claimed is:
 1. An active clamp circuit for a power converter having a transformer, comprising: an active clamp switch having a drain node, a gate node, and a source node, the drain node being configured to be directly electrically connected to a first terminal of a primary winding of the transformer; an active clamp capacitor having a first terminal directly electrically connected to the source node of the active clamp switch, and a second terminal configured to be directly electrically connected to a second terminal of the primary winding; a gate driver circuit coupled to the gate node to control the active clamp switch, the gate driver circuit having a high-side input voltage node and a low-side input voltage node, the low-side input voltage node being coupled to the first terminal of the active clamp capacitor; and a linear voltage regulator circuit configured to: i) receive an input voltage from the second terminal of the active clamp capacitor, and ii) provide a linearly regulated voltage to the high-side input voltage node of the gate driver circuit using the input voltage, the linearly regulated voltage being of a sufficient voltage level to control the active clamp switch.
 2. The active clamp circuit of claim 1, further comprising: a second capacitor electrically coupled between the high-side input voltage node and the low-side input voltage node of the gate driver circuit.
 3. The active clamp circuit of claim 1, wherein: the linearly regulated voltage provided by the voltage regulator circuit is of a lower voltage level than that of the input voltage received by the voltage regulator circuit; and the linear voltage regulator circuit comprises an LDO.
 4. The active clamp circuit of claim 1, wherein: the active clamp switch, the voltage regulator circuit, and the gate driver circuit are integrated into a single integrated circuit (IC).
 5. The active clamp circuit of claim 1, wherein: the second terminal of the active clamp capacitor is configured to be coupled to a drain node of another switch; and the active clamp circuit is configured to limit a voltage at the drain node of the other switch to a maximum voltage.
 6. The active clamp circuit of claim 5, wherein: the drain node of the other switch is coupled to the second terminal of the primary winding of the transformer; and the other switch controls a current through the primary winding of the transformer.
 7. The active clamp circuit of claim 1, wherein: the drain node of the active clamp switch is configured to be electrically connected to a DC voltage input node of the power converter.
 8. The active clamp circuit of claim 7, wherein: the active clamp capacitor is configured to be charged by a current originating at the second terminal of the primary winding of the transformer and flowing to the DC voltage input node via the active clamp capacitor and a body-diode of the active clamp switch.
 9. The active clamp circuit of claim 8, wherein: the second terminal of the active clamp capacitor is configured to be coupled to a drain node of another switch; the drain node of the other switch is coupled to the second terminal of the primary winding of the transformer; the other switch controls a current through the primary winding of the transformer; and the active clamp capacitor is configured to be charged by the current originating at the second terminal of the primary winding of the transformer when the other switch is turned off.
 10. The active clamp circuit of claim 1, wherein: the drain node of the active clamp switch is configured to be electrically connected to a DC voltage input node of the power converter, the DC voltage input node having a DC voltage that is relative to a ground voltage node of the power converter; and the low-side input voltage node of the gate driver circuit is offset in voltage relative to a voltage of the ground voltage node.
 11. The active clamp circuit of claim 10, wherein: the second terminal of the active clamp capacitor is configured to be connected to a drain node of another switch; and a source node of the other switch is configured to be connected to the ground voltage node.
 12. A power converter comprising: a transformer having a primary winding and a secondary winding, a first terminal of the primary winding being configured to be coupled to a DC voltage input node, the secondary winding being configured to be coupled to a load; a main switch coupled to a second terminal of the primary winding to control a current through the primary winding; and an active clamp circuit comprising: an active clamp switch having a drain node, a gate node, and a source node, the drain node being configured to be directly electrically connected to the first terminal of the primary winding of the transformer; an active clamp capacitor having a first terminal directly electrically connected to the source node of the active clamp switch, and a second terminal configured to be directly electrically connected to the second terminal of the primary winding; a gate driver circuit coupled to the gate node to control the active clamp switch, the gate driver circuit having a high-side input voltage node and a low-side input voltage node, the low-side input voltage node being coupled to the first terminal of the active clamp capacitor; and a linear voltage regulator circuit configured to: i) receive an input voltage from the second terminal of the active clamp capacitor, and ii) provide a linearly regulated voltage to the high-side input voltage node of the gate driver circuit using the input voltage, the linearly regulated voltage being of a sufficient voltage level to control the active clamp switch.
 13. The power converter of claim 12, further comprising: a second capacitor electrically coupled between the high-side input voltage node and the low-side input voltage node of the gate driver circuit.
 14. The power converter of claim 12, wherein: the active clamp switch, the voltage regulator circuit, and the gate driver circuit are integrated into a single integrated circuit (IC).
 15. The power converter of claim 12, wherein: the active clamp circuit clamps a voltage at a drain node of the main switch to a maximum voltage.
 16. The power converter of claim 12, wherein: the drain node of the active clamp switch is configured to be electrically connected to the DC voltage input node of the power converter.
 17. The power converter of claim 16, wherein: the active clamp capacitor is configured to be charged by a current originating at the second terminal of the primary winding and flowing to the DC voltage input node via the active clamp capacitor and a body-diode of the active clamp switch.
 18. The power converter of claim 17, wherein: the active clamp capacitor is configured to be charged by the current originating at the second terminal of the primary winding of the transformer when the main switch is turned off.
 19. The power converter of claim 12, wherein: the drain node of the active clamp switch is configured to be electrically connected to the DC voltage input node of the power converter, the DC voltage input node having a DC voltage that is relative to a ground voltage node of the power converter; and the low-side input voltage node of the gate driver circuit is offset in voltage relative to a voltage of the ground voltage node.
 20. The power converter of claim 19, wherein: a source node of the main switch is configured to be connected to the ground voltage node. 